Fluid energy reduction device

ABSTRACT

A fluid energy reduction device especially for a flow control valve has a fluid inlet and a fluid outlet separated by a plurality of stacked plates in the form of a trim stack. Each plate of the stack has a plurality of rows of discrete, spaced columns that extend to the plate above in the stack. Fluid flowing through the trim stack is obstructed by the columns and is forced to divide into a plurality of subordinate flow paths. The rows of columns are staggered in such a way that fluid downstream of the first row of columns is incident directly on columns of the next row. The arrangement provides for the smooth pressure drop and energy reduction in the fluid without cavitation, noise or vibration.

The present invention relates to a fluid energy reduction device and toa valve or regulator in which fluid passing therethrough is subjected toa pressure drop and energy reduction by a such a device.

It is known in high pressure fluid flow control systems to have controldevices that are designed to effect a pressure drop in the fluid passingtherethrough. For a given fluid pressure drop across such a device thereis a corresponding increase in fluid velocity that must be carefullymanaged. Moreover, pressure drops occurring at high fluid flow rates invalves or the like are generally accompanied by other problems such aserosion, noise, vibration and cavitation.

A common solution to the above problems is to divide the flow throughthe device into a plurality of separate streams, each of which is in theform of a tortuous path. The fluid pressure and energy of the fluid ispartially dissipated along such paths as a result of losses caused byfriction between walls of the path, rapid changes in fluid direction andexpansion or contraction chambers.

In fluid control valves such control devices usually take the form of astack of discs or a plurality of concentric cylindrical sleeves. In theformer design the fluid path is defined by tortuous passages machinedinto one or both facing surfaces of adjacent discs. In the latter designthe sleeves are radially perforated with the perforations of adjacentsleeves being offset to cause the fluid to flow in a tortuous path. Thesleeves may be separated by intermediate annular passages which allowthe fluid passing therethrough to expand before it then has to contractto pass through the perforations of the next sleeve. The specificgeometric arrangement of such designs can be configured as desired toallow the pressure of the fluid of each stream to drop in relativelysmall increments and in many stages.

Examples of fluid control devices of the kind described above aredisclosed in U.S.-RE-32,197, GB-A-2335054 and U.S. Pat. No. 5,390,896.

Valves of the kind described above are generally fitted with a plug thatis movable within a central cylindrical cavity defined in the discs orinside the innermost of the concentric sleeves. The plug is axiallymovable within the cavity to close or open the exits to the fluid pathsso as to vary the number of paths that are available for fluid flow inaccordance with the flow characteristics required by die user.

Although such fluid control devices are effective their construction andtherefore manufacture and assembly is complex and expensive. Moreover,the presence of tortuous paths with sharp bends increases the tendencyfor clogging and erosion caused by the presence of small particles (suchas dirt, sand, grit and other detritus) in the fluid flow.

It is an object of the present invention to obviate or mitigate theaforesaid disadvantages.

According to a first aspect of the present invention there is provided afluid energy reduction device comprising a fluid inlet and a fluidoutlet separated by a plurality of stacked plates between adjacent pairsof which are defined fluid flow paths, wherein at least one of the pathsis divided into subordinate paths by a plurality of rows of discrete,spaced flow obstructing members that extend between adjacent plates.

By using flow obstructing members the fluid is presented with severalalternative paths and the absence of a single tortuous path with areasof fluid recirculation reduces or eliminates the problem of erosion bydetritus in the fluid flow.

The flow obstructing members may have any convenient shape in crosssection and may vary in shape across the plate although in preferredembodiments at least part of the surface of the obstructing member inthe fluid flow path is arcuate to allow smooth passage of fluid flowaround the obstructing member. The flow obstructing members, beingspaced and discrete, serve to separate incident fluid into separatestreams that then pass around the obstructing member and recombinedownstream before being separated again when incident on an obstructingmember in a subsequent row. The separation and convergence of the flowtogether with the usual frictional drag effects cause a smooth pressuredrop and therefore energy reduction in the fluid. By increasing thenumber of rows the repeated separation and convergence imparts a greaterpressure reduction.

In a preferred embodiment the flow obstructing members of one row areoffset laterally from those of an adjacent row in the direction of fluidflow. This arrangement is designed to ensure that the downstream flowsof fluid from one row are directed to be incident directly on theobstructing members of the subsequent row.

The flow obstructing members may be formed on the surface of each plateand may be integral therewith. In an alternative embodiment the platesand flow obstructing members are defined by an assembly of elongatemembers whose configuration comprises plate elements interspersedaxially along the length of the elongate member with the flowobstructing members, the plate elements of adjacent elongate memberscombining to form said plate when said elongate members are assembled.

In one preferred embodiment the flow obstructing members are generallycircular in cross section and decrease in cross section area from row torow in the direction of fluid flow from inlet to outlet. In anotherpreferred embodiment the flow obstructing members increase in crosssectional area from inlet to outlet.

Each plate may have a plurality of spaced flow paths defined thereon.

In a preferred embodiment the plates are annular and have a centralcircular aperture. The rows of flow obstructing members are annular andarranged in a concentric configuration. The plate may be divided into aplurality of angularly spaced radially extending flow paths.

According to a second aspect of the present invention there is provideda fluid control valve comprising a fluid energy reduction device of thekind defined above and a valve control member reciprocally disposed insaid device.

Specific embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings inwhich:

FIG. 1 is a longitudinal section through a fluid control valve fittedwith a fluid energy reduction device of the present invention;

FIG. 2 is a perspective view of a valve trim stack of FIG. 1;

FIG. 3 is a perspective view from above of a cut-away section of thetrim stack of FIG. 2;

FIG. 4 is diagrammatic representation of fluid flow through a part of adisc of the trim stack of FIG. 2;

FIG. 5 is diagrammatic representation in plan of one embodiment fluidflow through a disc of the trim stack;

FIG. 6 is a diagrammatic representation in plan of an alternativeembodiment of fluid flow through a disc of the trim stack;

FIG. 7 is a perspective view from above of a cut away section—of analternative embodiment of the trim stack;

FIG. 8 is a plan view of a disc from the trim stack of FIG. 7;

FIG. 9 is a plan view of an alternative embodiment of a disc of a trimstack in accordance with the present invention;

FIG. 10 is a close up view of part of the disc of FIG. 9; and

FIG. 11 is a perspective view of the construction of part of trim stackusing a plurality of the discs shown in FIG. 9.

Referring now to FIG. 1 of the drawings, the control valve comprises avalve body 10 defining inlet and outlet conduits 11, 12 that in use areconnected to pipes (not shown) that transport the fluid to and from thevalve. The valve is intended to be bi-directional in that the directionof fluid flow can be the reverse of that shown in the figures. Thechoice of fluid flow direction is dependent on the particularapplication.

Between the inlet and outlet conduits 11, 12 the housing defines agenerally circular central chamber in which is removably received a trimstack 13. The stack 13 is disposed on a valve seat 14 and comprises aplurality of coaxial plate-like discs 15 (described in detail below) ofidentical size, each disc 15 having a central circular aperture 16. Avalve cover 17 is fixed to the valve body 10 by bolts 18 so as to closethe chamber and retain the stack 13 in place.

In combination the stack of discs define a cylindrical bore 19 in whicha reciprocal plug 20 is slidably disposed. The plug 20 is attached toone end of an elongate stem 21 that extends upwardly through a bore 22in the cover 17 via a guide seal 23 and is reciprocal by means of anactuator (not shown) connected to the other end of the stem 21 and tothe exterior of the valve cover 17.

The plug 20 is selectively moveable in an axial direction between afully open position in which fluid flowing through the valve from theinlet to outlet conduits 11, 12 passes through the trim stack 13, and aclosed position where it is in abutment with the valve seat 14 andblocks flow through the stack 13. Between these two positions the plug20 acts as a throttle by permitting only a predetermined volume of fluidflow and thereby determining the characteristics of the valveperformance.

The trim stack 13 is shown in more detail in FIG. 2. The stackeddiscs-15 are retained between upper and lower stack plates 24, 25 thatare configured to fit the corresponding mating surfaces of the valveseat 14 and valve body 10.

As can be seen from FIG. 3 each disc 15 in the stack 13 has a pluralityof radial flow passages 26 equi-angularly spaced around its surface.Each passage 26 is in the form of a rectilinear duct cut into thesurface of the disc 15. Projecting from the bottom surface of the ductis a plurality of discrete spaced columns 27 formed integrally in thedisc 15 in concentric annular rows 28. In the exemplary embodiment shownin FIG. 3 the columns 27 are circular in cross section and reduce incross sectional area from row to row in the fluid flow direction(indicated by the arrow). The columns 27 are staggered in such a waythat those of any particular row 28 are circumferentially offset fromthose in the preceding and subsequent rows. The discs 15 may be machinedinto or cast in this configuration.

The fluid flow into the trim stack 13 is incident on the first row 28 ofcolumns 27 in each passage 26 and is divided into a plurality of smallerflow paths 29 that pass between adjacent columns 27 as can be seen inFIG. 4. As the fluid progresses to subsequent rows 28 it is again forcedto divide as it passes around the front of the column 27. However, thereis a convergence of the smaller flows 29 downstream of the column 27.The staggering of the columns between adjacent rows is designed todirect the downstream fluid flow from between the columns of one rowdirectly into the path of a column of the next row. This constant fluidflow separation, subsequent recombination and the frictional dragbetween the fluid and the curved surfaces of the columns 27 serves toreduce the energy and therefore pressure of the fluid in stages therebyproviding a smooth pressure drop across the trim stack 13.

It is to be appreciated that the specific design of the trim stack discs15 can be varied according to the particular application, the flowdirection and the flow characteristics that are required. Examples ofdiscs with four and six radial passages are shown in FIGS. 5 and 6respectively. The spacing between columns 27 may increase from row torow in applications where it is necessary to increase the fluid flowarea through the flow passage 26.

An alternative embodiment of the surface configuration of the disc isshown in FIGS. 7 and 8 in which parts corresponding to those of FIGS. 3and 4 are represented by the same reference numerals increased by 100and are not described except insofar as they differ from theircounterparts. In this embodiment the fluid flow direction is reversed.The disc 115 surface is not divided into separate passages and columns127 are disposed over the full surface of the disc 115. The columns 127vary in cross sectional shape from row to row 128 and becomeprogressively elongated (into lozenge shapes) in the circumferentialdirection towards the outer periphery of the disc 115. The arrangementof the columns 127 and their distortion is designed to maintain therequired flow area and resistance across the trim stack 113.

Referring now back to FIGS. 1 to 3, as the valve plug 20 is moved up ordown the central bore 19 it covers or uncovers the fluid passages 26 ineach disc 15 so as to increase or reduce fluid communication between theinlet and outlet conduits 11, 12.

A further alternative embodiment is shown in FIGS. 9 to 11 in which theflow passages in the trim stack are each formed by a plurality ofmachined bars. Parts corresponding to those of FIGS. 3 and 4 arerepresented by the same reference numerals increased by 200 and are notdescribed except insofar as they differ from their counterparts Each bar200 comprises, in vertical array, a plurality of hexagonal segments 201interspersed by cylindrical columns 227. When the bars 200 are assembledinto groups the hexagonal segments 201 at a given vertical level on eachbar combine to form the base walls of the fluid passage ducts 226 for agiven tier of the stack 213 and the columns 227 provide the samefunction as those described above in relation to FIGS. 3 to 6. Thethickness of each hexagonal segment 201 is the same as the thickness ofthe discs 15 at the flow ducts 26 described above. The groups of bars200 are assembled into rectangular blocks 202 and are interspersed bysolid cylindrical segments 203 of metal so as to complete the trim stack213. The whole assembly is held together by a cage (not shown).

It will be appreciated that numerous modifications to theabove-described design may be made without departing from the scope ofthe invention as defined in the appended claims. For example, althoughthe trim stack is depicted in the accompanying drawings as generallycylindrical other shapes may be used. Moreover the columns of any of theembodiments can be of any suitable cross section shape and divided intoany number of separate passages. The number of rows of columns on eachdisc is determined by the pressure drop required across the trim stack,the higher the pressure drop required the greater the number of rowsrequired to dissipate energy safely within the trim stack. The columnsneed not be integral with the discs but may alternatively comprise pinsor pegs that are received in through bores or blind holes in the discsurface. The single pin or peg may pass through one or more discs toprovide columns that ale common to one or more discs in the stack.

1. A fluid energy reduction device comprising a fluid inlet and a fluidoutlet separated by a plurality of stacked plates between adjacent pairsof which are defined fluid flow paths, each plate having a plurality ofspaced flow paths defined thereon, wherein at least one of the paths isdivided into subordinate paths by a plurality of rows of discrete,spaced flow-obstructing members that extend between adjacent plates. 2.A fluid energy reduction device according to claim 1, wherein theobstructing members of one row are laterally offset from those of anadjacent row in the direction of the fluid flow path.
 3. A fluid energyreduction device according to claim 1, wherein at least part of asurface of the obstructing members in the fluid flow path is arcuate soas to allow smooth passage of fluid flow therearound.
 4. A fluid energyreduction device according to claim 1, wherein the obstructing membersare generally circular in cross section.
 5. A fluid energy reductiondevice according to claim 1, wherein the cross-sectional area of theobstructing members increases across the rows from inlet to outlet.
 6. Afluid energy reduction device according to claim 1, wherein thecross-sectional area of the obstructing members decreases across therows from inlet to outlet.
 7. A fluid energy reduction device accordingto claim 1, wherein the flow obstructing members are formed on a surfaceof each plate.
 8. A fluid energy reduction device according to claim 1,wherein the plates and flow obstructing members are defined by anassembly of elongate members, each elongate member having along itslength plate elements interspersed with said flow obstructing members,the plate elements of adjacent elongate members combining to form saidplate when the elongate members are assembled.
 9. A fluid energyreduction device according to claim 8, wherein the elongate members areassembled in parallel.
 10. A fluid energy reduction device according toclaim 9, wherein each plate has a plurality of spaced flow paths definedthereon.
 11. A fluid energy reduction device according to claim 10,wherein the plates are annular and have a central circular aperture. 12.A fluid energy reduction device according to claim 11, wherein the plateis divided into a plurality of angularly spaced radially extending flowpaths.
 13. A fluid control valve comprising a fluid energy reductiondevice according to claim 1 and a valve control member reciprocallydisposed in said device.
 14. (canceled)
 15. (canceled)
 16. A fluidenergy reduction device according to claim 2, wherein at least part of asurface of the obstructing members in the fluid flow path is arcuate soas to allow smooth passage of fluid flow therearound.
 17. A fluid energyreduction device according to claim 2, wherein at least part of asurface of the obstructing members in the fluid flow path is arcuate soas to allow smooth passage of fluid flow therearound; wherein theobstructing members are generally circular in cross section; wherein thecross-sectional area of the obstructing members increases across therows from inlet to outlet; wherein the flow obstructing members areformed on a surface of each plate; and, wherein the plates and flowobstructing members are defined by an assembly of elongate members, eachelongate member having along its length plate elements interspersed withsaid flow obstructing members, the plate elements of adjacent elongatemembers combining to form said plate when the elongate members areassembled.
 18. A fluid energy reduction device according to claim 2,wherein at least part of a surface of the obstructing members in thefluid flow path is arcuate so as to allow smooth passage of fluid flowtherearound; wherein the obstructing members are generally circular incross section; wherein the cross-sectional area of the obstructingmembers decreases across the rows from inlet to outlet; wherein the flowobstructing members are formed on a surface of each plate; and, whereinthe plates and flow obstructing members are defined by an assembly ofelongate members, each elongate member having along its length plateelements interspersed with said flow obstructing members, the plateelements of adjacent elongate members combining to form said plate whenthe elongate members are assembled.
 19. (canceled)
 20. A fluid energyreduction device according to claim 1, wherein the plates are annularand have a central circular apertive.